1. Field of the Invention
This invention relates to a magnetic erasing head, and more particularly to a magnetic erasing head suitable for a magnetic recording medium having high coercive force.
2. Description of the Prior Art
A magnetic recording tape having high coercive force is required for high-density magnetic recording. At the present, an AC magnetic erasing head made of ferrite is usually used for erasing signals recorded on the magnetic recording tape. However, there are such problems in the use of the conventional AC magnetic erasing head that it cannot sufficiently erase the recorded signals from the magnetic recording tape, and that much power should be consumed for erasing the recorded signals by it.
For example, FIG. 1 shows schematically a conventional magentic erasing head 1 of the semi-double gap type, and FIG. 2 shows schematically another conventional magnetic erasing head 2 of the double gap type. The magnetic erasing heads 1 and 2 are made of ferrite. The front surfaces of the magnetic erasing heads 1 and 2 to be contacted with the magnetic recording tape are further worked or polished. However, the front surfaces of the magnetic erasing heads 1 and 2 shown in FIG. 1 and FIG. 2 are not yet worked or polished.
The magnetic erasing head 1 of FIG. 1 includes two core elements 3a and 3b made of ferrite. Two front gaps 5 and 6 are formed between the core elements 3a and 3b. The core elements 3a and 3b are set to each other, for example, by resin material R such as epoxy resin. An erasing coil 9 is wound on the central portion of the one core element 3a.
The other magnetic erasing head 2 of FIG. 2 includes three core elements 4a, 4b and 4c constituting the so-called "E-shape" type, made of ferrite. The core elements 4a, 4b and 4c are integrally formed with each other. Two front gaps 7 and 8 are formed between the side core elements 4a, 4c and the central core element 4b in the magnetic erasing head 2. An erasing coil 10 is would on the central core element 4b.
In FIG. 1 and FIG. 2, the depth of the pole faces of the core elements 3a, 4a and 4c is usually about 300.mu.. However, FIG. 1 and FIG. 2 do not show the actual size relationships between the parts for facilitation of the understanding. For example, the ratio of the length of the front gap to the depth of the pole face is 1/2.
When the erasing coils 9 and 10 are energized with AC power, alternating magnetic fluxes are generated in the front gaps 5, 6, 7 and 8. The recorded signals on the magnetic recording tape are erased by the alternating magnetic fluxes of the gaps 5, 6, 7 and 8. The magnetic fluxes are concentrated in the gaps 5, 6, 7 and 8. The magnetic flux densities are higher in the gaps 5, 6, 7 and 8. Particularly, when the recorded signals are erased from the magnetic recording tape having high coercive force by the magnetic erasing head 1 or 2, the magnetic flux density becomes extremely high in the gaps 5 and 6, or 7 and 8. Generally, the saturation magnetic flux density of ferrite material is low. Accordingly, the core elements 3a, 4a and 4c are liable to be saturated with the magnetic fluxes particularly at the edge portions. In the saturation, the amounts of the magnetic fluxes from the core elements 3a, 4a and 4c are supressed, and much electric power is consumed in vain.